Electrosurgical instrument and method of use

ABSTRACT

An electrosurgical medical device and method for creating thermal welds in engaged tissue. In one embodiment, at least one jaw of the instrument defines a tissue engagement plane carrying a conductive-resistive matrix of a conductively-doped non-conductive elastomer. The engagement surface portions thus can be described as a positive temperature coefficient material that has a unique selected decreased electrical conductance at each selected increased temperature thereof over a targeted treatment range. The conductive-resistive matrix can be engineered to bracket a targeted thermal treatment range, for example about 60° C. to 80° C., at which tissue welding can be accomplished. In one mode of operation, the engagement plane will automatically modulate and spatially localize ohmic heating within the engaged tissue from Rf energy application—across micron-scale portions of the engagement surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-in-Part of co-pending U.S.patent application Ser. No. 10/032,867 filed Oct. 22, 2001 (Docket No.SRX-011) titled Electrosurgical Jaw Structure for Controlled EnergyDelivery. This application also is related to U.S. patent applicationSer. No. 09/721,812 filed Nov. 24, 2000 (Docket No. SCI-011) titledPolymer Embolic Elements with Metallic Coatings for Occlusion ofVascular Malformations, which is incorporated herein by this reference.This application also is related to: Provisional U.S. Patent ApplicationSerial No. 60/337,695 filed Dec. 3, 2001 (Docket No. SRX-012) titledElectrosurgical Jaw Structure for Controlled Energy Delivery;Provisional U.S. Patent Application Serial No. 60/347,382 filed Jan. 11,2002 (Docket No. SRX-013) titled Jaw Structure for ElectrosurgicalInstrument and Method of Use; Provisional U.S. Patent Application SerialNo. 60/351,517 filed Jan. 22, 2002 (Docket No. SRX-014) titledElectrosurgical Instrument and Method of Use, and Provisional U.S.Patent Application Serial No. 60/366,992 filed Mar. 20, 2002 (Docket No.SRX-015) titled Electrosurgical Instrument and Method of Use all, ofwhich are incorporated herein by this reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to medical devices and techniques and moreparticularly relates to working ends of electrosurgical instruments thatcan apply energy to tissue from an engagement surface that can, ineffect, independently modulate the Rf power level applied to tissueacross localized micro-scale portions of the engagement surface, the Rfenergy being delivered from a single source.

[0004] 2. Description of the Related Art

[0005] In the prior art, various energy sources such as radiofrequency(Rf) sources, ultrasound sources and lasers have been developed tocoagulate, seal or join together tissues volumes in open andlaparoscopic surgeries. The most important surgical application relatesto sealing blood vessels that contain considerable fluid pressuretherein. In general, no instrument working ends using any energy sourcehave proven reliable in creating a “tissue weld” or “tissue fusion” thathas very high strength immediately post-treatment. For this reason, thecommercially available instruments, typically powered by Rf orultrasound, are mostly limited to use in sealing small blood vessels andtissues masses with microvasculature therein. The prior art Rf devicesalso fail to provide seals with substantial strength in anatomicstructures having walls with irregular or thick fibrous content, inbundles of disparate anatomic structures, in substantially thickanatomic structures, or in tissues with thick fascia layers (e.g., largediameter blood vessels).

[0006] In a basic bi-polar Rf jaw arrangement, each face of opposingfirst and second jaws comprises an electrode and Rf current flows acrossthe captured tissue between the opposing polarity electrodes. Such priorart Rf jaws that engage opposing sides of tissue typically cannot causeuniform thermal effects in the tissue-whether the captured tissue isthin or substantially thick. As Rf energy density in tissue increases,the tissue surface becomes desiccated and resistant to additional ohmicheating. Localized tissue desiccation and charring can occur almostinstantly as tissue impedance rises, which then can result in anon-uniform seal in the tissue. The typical prior art Rf jaws can causefurther undesirable effects by propagating Rf density laterally from theengaged tissue thus causing unwanted collateral thermal damage.

[0007] The commercially available Rf sealing instruments typically useone of two approaches to “control” Rf energy delivery in tissue. In afirst “power adjustment” approach, the Rf system controller can rapidlyadjust the level of total power delivered to the jaws' engagementsurfaces in response to feedback circuitry coupled to the activeelectrodes that measures tissue impedance or electrode temperature. In asecond “current-path directing” approach, the instrument jaws carry anelectrode arrangement in which opposing polarity electrodes are spacedapart by an insulator material—which may cause current to flow within anextended path through captured tissue rather that simply betweensurfaces of the first and second jaws. Electrosurgical graspinginstruments having jaws with electrically-isolated electrodearrangements in cooperating jaws faces were proposed by Yates et al. inU.S. Pat. Nos. 5,403,312; 5,735,848 and 5,833,690.

[0008] The illustrations of the wall of a blood vessel in FIGS. 1A-1Dare useful in understanding the limitations of prior art Rf working endsfor sealing tissue. FIG. 1B provides a graphic illustration of theopposing vessel walls portions 2 a and 2 b with the tissue divided intoa grid with arbitrary micron dimensions—for example, the grid canrepresent 5 microns on each side of the targeted tissue. In order tocreate the most effective “weld” in tissue, each micron-dimensionedvolume of tissue must be simultaneously elevated to the temperatureneeded to denature proteins therein. As will be described in more detailbelow, in order to create a “weld” in tissue, collagen, elastin andother protein molecules within an engaged tissue volume must bedenatured by breaking the inter- and intra-molecular hydrogenbonds—followed by re-crosslinking on thermal relaxation to create afused-together tissue mass. It can be easily understood that ohmicheating in tissue—if not uniform—can at best create localized spots oftruly “welded” tissue. Such a non-uniformly denatured tissue volumestill is “coagulated” and will prevent blood flow in small vasculaturethat contains little pressure. However, such non-uniformly denaturedtissue will not create a seal with significant strength, for example in2 mm. to 10 mm. arteries that contain high pressures.

[0009] Now turning to FIG. 1C, it is reasonable to ask whether the“power adjustment” approach to energy delivery is likely to cause auniform temperature within every micron-scale tissue volume in the gridsimultaneously—and maintain that temperature for a selected timeinterval. FIG. 1C shows the opposing vessel walls 2 a and 2 b beingcompressed with cut-away phantom views of opposing polarity electrodeson either side of the tissue. One advantage of such an electrodearrangement is that 100% of each jaw engagement surface comprises an“active” conductor of electrical current—thus no tissue is engaged by aninsulator which theoretically would cause a dead spot (no ohmic heating)proximate to the insulator. FIG. 1C graphically depicts current “paths”p in the tissue at an arbitrary time interval that can be microseconds(us) apart. Such current paths p would be random and constantly influx-along transient most conductive pathways through the tissue betweenthe opposing polarity electrodes. The thickness of the “paths” isintended to represent the constantly adjusting power levels. If oneassumes that the duration of energy density along any current path p iswithin the microsecond range before finding a new conductive path—andthe thermal relaxation time of tissue is the millisecond (ms) range,then what is the likelihood that such entirely random current paths willrevisit and maintain each discrete micron-scale tissue volume at thetargeted temperature before thermal relaxation? Since the hydration oftissue is constantly reduced during ohmic heating—any regions of moredesiccated tissue will necessarily lose its ohmic heating and will beunable to be “welded” to adjacent tissue volumes. The “power adjustment”approach probably is useful in preventing rapid overall tissuedesiccation. However, it is postulated that any approach that relies onentirely “random” current paths p in tissue—no matter the powerlevel—cannot cause contemporaneous denaturation of tissue constituentsin all engaged tissue volumes and thus cannot create an effectivehigh-strength “weld” in tissue.

[0010] Now referring to FIG. 1D, it is possible to evaluate the second“current-path directing” approach to energy delivery in a jaw structure.FIG. 1D depicts vessel walls 2 a and 2 b engaged between opposing jawssurfaces with cutaway phantom views of opposing polarity (+) and (−)electrodes on each side of the engaged tissue. An insulator indicated at10 is shown in cut-away view that electrically isolates the electrodesin the jaw. One significant disadvantage of using an insulator 10 in ajaw engagement surface is that no ohmic heating of tissue can bedelivered directly to the tissue volume engaged by the insulator 10 (seeFIG. 1D). The tissue that directly contacts the insulator 10 will onlybe ohmically heated when a current path p extends through the tissuebetween the spaced apart electrodes. FIG. 1D graphically depicts currentpaths p at any arbitrary time interval, for example in the μs range.Again, such current paths p will be random and in constant flux alongtransient conductive pathways.

[0011] This type of random, transient Rf energy density in paths pthrough tissue, when any path may occur only for a microsecond interval,is not likely to uniformly denature proteins in the entire engagedtissue volume. It is believed that the “current-path directing” approachfor tissue sealing can only accomplish tissue coagulation or seals withlimited strength.

[0012] Now turning to FIG. 2, it can be conceptually understood that thekey requirements for thermally-induced tissue welding relate to: (i)means for “non-random spatial localization” of energy densities in theengaged tissue et, (ii) means for “controlled, timed intervals” of powerapplication of such spatially localized of energy densities, and (iii)means for “modulating the power level” of any such localized,time-controlled applications of energy.

[0013]FIG. 2 illustrates a hypothetical tissue volume with a lower jaw'sengagement surface 15 backed away from the tissue. The tissue is engagedunder very high compression which is indicated by arrows in FIG. 2. Theengagement surface 15 is shown as divided into a hypothetical grid of“pixels” or micron-dimensioned surface areas 20. Thus, FIG. 2graphically illustrates that to create an effective tissue weld, thedelivery of energy should be controlled and non-randomly spatiallylocalized relative to each pixel 20 of the engagement surface 15.

[0014] Still referring to FIG. 2, it can be understood that there aretwo modalities in which spatially localized, time-controlled energyapplications can create a uniform energy density in tissue for proteindenaturation. In a first modality, all cubic microns of the engagedtissue (FIG. 2) can be elevated to the required energy density andtemperature contemporaneously to create a weld. In a second modality, a“wave” of the required energy density can sweep across the engagedtissue et that can thereby leave welded tissue in its wake. The authorshave investigated, developed and integrated Rf systems for accomplishingboth such modalities—which are summarized in the next Section.

SUMMARY OF THE INVENTION

[0015] The systems and methods corresponding to invention relate tocreating thermal “welds” or “fusion” within native tissue volumes. Thealternative terms of tissue “welding” and tissue “fusion” are usedinterchangeably herein to describe thermal treatments of a targetedtissue volume that result in a substantially uniform fused-togethertissue mass that provides substantial tensile strength immediatelypost-treatment. Such tensile strength (no matter how measured) isparticularly important (i) for welding blood vessels in vesseltransection procedures, (ii) for welding organ margins in resectionprocedures, (iii) for welding other anatomic ducts wherein permanentclosure is required, and also (iv) for vessel anastomosis, vesselclosure or other procedures that join together anatomic structures orportions thereof.

[0016] The welding or fusion of tissue as disclosed herein is to bedistinguished from “coagulation”, “sealing”, “hemostasis” and othersimilar descriptive terms that generally relate to the collapse andocclusion of blood flow within small blood vessels or vascularizedtissue. For example, any surface application of thermal energy can causecoagulation or hemostasis—but does not fall into the category of“welding” as the term is used herein. Such surface coagulation does notcreate a weld that provides any substantial strength in the affectedtissue.

[0017] At the molecular level, the phenomenon of truly “welding” tissueas disclosed herein may not be fully understood. However, the authorshave identified the parameters at which tissue welding can beaccomplished. An effective “weld” as disclosed herein results from thethermally-induced denaturation of collagen, elastin and other proteinmolecules in a targeted tissue volume to create a transient liquid orgel-like proteinaceous amalgam. A selected energy density is provided inthe targeted tissue to cause hydrothermal breakdown of intra- andintermolecular hydrogen crosslinks in collagen and other proteins. Thedenatured amalgam is maintained at a selected level of hydration—withoutdesiccation—for a selected time interval which can be very brief. Thetargeted tissue volume is maintained under a selected very high level ofmechanical compression to insure that the unwound strands of thedenatured proteins are in close proximity to allow their intertwiningand entanglement. Upon thermal relaxation, the intermixed amalgamresults in “protein entanglement” as re-crosslinking or renaturationoccurs to thereby cause a uniform fused-together mass.

[0018] To better appreciate the scale at which thermally-induced proteindenaturation occurs—and at which the desired protein entanglement andre-crosslinking follows—consider that a collagen molecule in its nativestate has a diameter of about 15 Angstroms. The collagen moleculeconsists of a triple helix of peptide stands about 1000 Angstroms inlength (see FIG. 2). In other words—a single μm³ (cubic micrometer) oftissue that is targeted for welding will contain 10's of thousands ofsuch collagen molecules. In FIG. 2, each tissue volume in the gridrepresents an arbitrary size from about 1 μm to 5 μm (microns). Elastinand other molecules targeted for denaturation are believed to be similarin dimension to collagen.

[0019] To weld tissue, or more specifically to thermally-induce proteindenaturation, and subsequent entanglement and re-crosslinking in atargeted tissue volume, it has been learned that the followinginterlinked parameters must be controlled:

[0020] (i) Temperature of thermal denaturation. The targeted tissuevolume must be elevated to the temperature of thermal denaturation,T_(d), which ranges from about 50° C. to 90° C., and more specificallyis from about 60° C. to 80° C. The optimal T_(d) within the largertemperature range is further dependent on the duration of thermaleffects and level of pressure applied to the engaged tissue.

[0021] (ii) Duration of treatment. The thermal treatment must extendover a selected time duration, which depending on the engaged tissuevolume, can range from less than 0.1 second to about 5 seconds. As willbe described below, the system of the in invention utilizes a thermaltreatment duration ranging from about 500 ms second to about 3000 ms.Since the objectives of protein entanglement occur at Td which can beachieved in ms (or even microseconds)—this disclosure will generallydescribe the treatment duration in ms.

[0022] (iii) Ramp-up in temperature; uniformity of temperature profile.There is no limit to the speed at which temperature can be ramped upwithin the targeted tissue. However, it is of utmost importance tomaintain a very uniform temperature across the targeted tissue volume sothat “all” proteins are denatured within the same microsecond interval.Only thermal relaxation from a uniform temperature T_(d) can result incomplete protein entanglement and re-crosslinking across an entiretissue volume. Without such uniformity of temperature ramp-up andrelaxation, the treated tissue will not become a fused-together tissuemass—and thus will not have the desired strength.

[0023] Stated another way, it is necessary to deposit enough energy intothe targeted volume to elevate it to the desired temperature T_(d)before it diffuses into adjacent tissue volumes. The process of heatdiffusion describes a process of conduction and convection and defines atargeted volume's thermal relaxation time (often defined as the timeover which the temperature is reduced by one-half). Such thermalrelaxation time scales with the square of the diameter of the treatedvolume in a spherical volume, decreasing as the diameter decreases. Ingeneral, tissue is considered to have a thermal relaxation time in therange of 1 ms. In a non-compressed tissue volume, or lightly compressedtissue volume, the thermal relaxation of tissue in an Rf applicationtypically will prevent a uniform weld since the random current pathsresult in very uneven ohmic heating (see FIGS. 1C-1D).

[0024] (iv) Instrument engagement surfaces. The instrument's engagementsurface(s) must have characteristics that insure that every squaremicron of the instrument surface is in contact with tissue during Rfenergy application. Any air gap between an engagement surface and tissuecan cause an arc of electrical energy across the insulative gap thusresulting in charring of tissue. Such charring (desiccation) willentirely prevent welding of the localized tissue volume and result infurther collateral effects that will weaken any attempted weld. For thisreason, the engagement surfaces corresponding to the invention are (i)substantially smooth at a macroscale, and (ii) in some cases at leastpartly of an elastomeric matrix that can conform to the tissue surfacedynamically during treatment. The jaw structure of the inventiontypically has gripping elements that are lateral from theenergy-delivering engagement surfaces. Gripping serrations otherwise cancause unwanted “gaps” and microscale trapped air pockets between thetissue and the engagement surfaces.

[0025] (v) Pressure. It has been found that very high externalmechanical pressures on a targeted tissue volume are critical in weldingtissue—for example, between the engagement surfaces of a jaw structure.In one aspect, as described above, the high compressive forces can causethe denatured proteins to be crushed together thereby facilitating theintermixing or intercalation of denatured protein stands whichultimately will result in a high degree of cross-linking upon thermalrelaxation.

[0026] In another aspect, the proposed high compressive forces, it isbelieved, can increase the thermal relaxation time of the engaged tissuepractically by an infinite amount. With the engaged tissue highlycompressed to the dimension of a membrane between opposing engagementsurfaces, for example to a thickness of about 0.001″, there iseffectively little “captured” tissue within which thermal diffusion cantake place. Further, the very thin tissue cross-section at the marginsof the engaged tissue prevents heat conduction to tissue volumes outsidethe jaw structure.

[0027] In yet another aspect, the high compressive forces at first causethe lateral migration of fluids from the engaged tissue which assists inthe subsequent welding process. It has been found that highly hydratedtissues are not necessary in tissue welding. What is important ismaintaining the targeted tissue at a selected level without desiccationas is typical in the prior art. Further, the very high compressiveforces cause an even distribution of hydration across the engaged tissuevolume prior to energy delivery.

[0028] In yet another aspect, the high compressive forces insure thatthe engagement planes of the jaws are in complete contact with thesurfaces of the targeted tissues, thus preventing any possibility of anarc of electrical energy a cross a “gap” would cause tissue charring, asdescribed previously.

[0029] One exemplary embodiment disclosed herein is particularly adaptedfor, in effect, independent spatial localization and modulation of Rfenergy application across micron-scale “pixels” of an engagementsurface. The jaw structure of the instrument defines opposing engagementplanes that apply high mechanical compression to the engaged tissue. Atleast one engagement plane has a surface layer that comprises first andsecond portions of a conductive-resistive matrix—preferably including anelastomer such as silicone (first portion) and conductive particles(second portion) distributed therein. An electrical source is coupled tothe working end such that the combination of the conductive-resistivematrix and the engaged tissue are intermediate opposing conductors thatdefine first and second polarities of the electrical source coupledthereto. The conductive-resistive matrix is designed to exhibit uniqueresistance vs. temperature characteristics, wherein the matrix maintainsa low base resistance over a selected temperature range with adramatically increasing resistance above a selected narrow temperaturerange.

[0030] In operation, it can be understood that current flow through theconductive-resistive matrix and engagement plane will apply active Rfenergy (ohmic heating) to the engaged tissue until the point in timethat any portion of the matrix is heated to a range that substantiallyreduces its conductance. This effect will occur across the surface ofthe matrix thus allowing each matrix “pixel” to deliver an independentlevel of power therethrough. This invention type of instant, localizedreduction of Rf energy application can be relied on to prevent anysubstantial dehydration of tissue proximate to the engagement plane. Thesystem eliminates the possibility of desiccation thus meeting another ofthe several parameters described above.

[0031] The conductive-resistive matrix and jaw body corresponding to theinvention further can provides a suitable cross-section and mass forproviding substantial heat capacity. Thus, when the matrix is elevatedin temperature to the selected thermal treatment range, the retainedheat of the matrix volume can effectively apply thermal energy to theengaged tissue volume by means of conduction and convection. Inoperation, the working end can automatically modulate the application ofenergy to tissue between active Rf heating and passive conductiveheating of the targeted tissue to maintain a targeted temperature level.

[0032] Of particular interest, another system embodiment disclosedherein is adapted for causing a “wave” of ohmic heating to sweep acrosstissue to denature tissue constituents in its wake. This embodimentagain utilizes at least one engagement plane in a jaw structure thatcarries a conductive-resistive matrix as described previously. At leastone of the opposing polarity conductors has a portion thereof exposed inthe engagement plane. The conductive-resistive matrix again isintermediate the opposing polarity conductors. When power delivery isinitiated, the matrix defines an “interface” therein where microcurrentsare most intense about the interface of the two polarities—since thematrix is not a simple conductor. The engaged tissue, in effect, becomesan extension of the interface of microcurrents created by thematrix—which thus localizes ohmic heating across the tissue proximatethe interface. The interface of polarities and microcurrents within thematrix will be in flux due to lesser conductance about the interface asthe matrix is elevated in temperature. Thus, a “wave-like” zone ofmicrocurrents between the polarities will propagate across thematrix—and across the engaged tissue. By this means of engaging tissuewith a conductive-resistive matrix, a wave of energy density can becaused to sweep across tissue to uniformly denature proteins which willthen re-crosslink to create a uniquely strong weld.

[0033] In general, the system of conductive-resistive matrices for Rfenergy delivery advantageously provides means for spatial-localizationand modulation of energy application from selected, discrete locations(“pixels”) across a single energy-emitting surface coupled to a singleenergy source

[0034] The system of conductive-resistive matrices for Rf energydelivery provides means for causing a dynamic wave of ohmic heating intissue to propagate across engaged tissue.

[0035] The system of conductive-resistive matrices for Rf energydelivery allows for opposing electrical potentials to be exposed in asingle engagement surface with a conductive matrix therebetween to allow100% of the engagement surface to emit energy to tissue.

[0036] The system of conductive-resistive matrices for Rf energyapplication to tissue allows for bi-polar electrical potential to beexposed in a single engagement surface without an intermediate insulatorportion.

[0037] The system of conductive-resistive matrices for energy deliveryallows for the automatic modulation of active ohmic heating and passiveheating by conduction and convection to treat tissue.

[0038] The system of conductive-resistive matrices for energyapplication to tissue advantageously allows for the creation of “welds”in tissue within about 500 ms to 2 seconds.

[0039] The system of conductive-resistive matrices for energyapplication to tissue provides “welds” in blood vessels that have veryhigh strength.

[0040] Additional objects and advantages of the invention will beapparent from the following description, the accompanying drawings andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1A is a view of a blood vessel targeted for welding.

[0042]FIG. 1B is a greatly enlarged sectional view of opposing wallportions of the blood vessel of FIG. 1A taken along line 1B-1B of FIG.1A.

[0043]FIG. 1C is a graphic representation of opposing walls of a bloodvessel engaged by prior art electrosurgical jaws showing random paths ofcurrent (causing ohmic heating) across the engaged tissue betweenopposing polarity electrodes.

[0044]FIG. 1D is a graphic representation of a blood vessel engaged byprior art electrosurgical jaws with an insulator between opposingpolarity electrodes on each side of the tissue showing random paths ofcurrent (ohmic heating).

[0045]FIG. 2 graphically represents a blood vessel engaged byhypothetical electrosurgical jaws under very high compression with anenergy-delivery surface proximate to the tissue.

[0046]FIG. 3A is a perspective view of a jaw structure oftissue-transecting and welding instrument that carries a Type “A”conductive-resistive matrix system corresponding to the invention.

[0047]FIG. 3B is a sectional view of the jaw structure of FIG. 3A takenalong line 3B-3B of FIG. 3A showing the location of conductive-resistivematrices.

[0048]FIG. 4 is a perspective view of another exemplary surgicalinstrument that carries a Type “A” conductive-resistive matrix systemfor welding tissue.

[0049]FIG. 5 is a sectional view of the jaw structure of FIG. 4 takenalong line 5-5 of FIG. 4 showing details of the conductive-resistivematrix.

[0050]FIG. 6 is a graph showing (i) temperature-resistance profiles ofalternative conductive-resistive matrices that can be carried in the jawof FIG. 5, (ii) the impedance of tissue, and (iii) the combinedresistance of the matrix and tissue as measured by a system controller.

[0051]FIG. 7A is an enlarged view of a portion of theconductive-resistive matrix and jaw body of FIG. 5 showing a firstportion of an elastomer and a second portion of conductive particles ata resting temperature.

[0052]FIG. 7B is another view the conductive-resistive matrix and jawbody of FIG. 7A after a portion is elevated to a higher temperature tomodulate microcurrent flow therethrough thus depicting a method of theinvention in spatially localizing and modulating Rf energy applicationfrom a conductive-resistive matrix that engages tissue.

[0053]FIG. 8A is a further enlarged view of the conductive-resistivematrix of FIG. 7A showing the first portion (elastomer) and the secondportion (conductive elements) and paths of microcurrents therethrough.

[0054]FIG. 8B is a further enlarged view of matrix of FIG. 7B showingthe effect of increased temperature and the manner in which resistanceto microcurrent flow is caused in the method of spatially localizing andmodulating Rf energy application.

[0055]FIG. 9 is an enlarged view of an alternative conductive-resistivematrix similar to that of FIG. 7A that is additionally doped withthermally conductive, electrically non-conductive particles.

[0056]FIG. 10 is an alternative jaw structure similar to that of FIGS. 5and 7A except carrying conductive-resistive matrices in the engagementsurfaces of both opposing jaws.

[0057]FIG. 11 is a greatly enlarged sectional view of the jaws of FIG.10 taken along line 11-11 of FIG. 10.

[0058]FIG. 12 is a sectional view of another exemplary jaw structurethat carries a Type “B” conductive-resistive matrix system for weldingtissue that utilizes opposing polarity electrodes with an intermediateconductive-resistive matrix in an engagement surface.

[0059]FIG. 13A is a sectional view of alternative Type “B” jaw with aplurality of opposing polarity electrodes with intermediateconductive-resistive matrices in the engagement surface.

[0060]FIG. 13B is a sectional view of a Type “B” jaw similar to that ofFIG. 13A with a plurality of opposing polarity electrodes withintermediate conductive-resistive matrices in the engagement surface ina different angular orientation.

[0061]FIG. 13C is a sectional view of another Type “B” jaw similar tothat of FIGS. 13A-13B with a plurality of opposing polarity electrodeswith intermediate matrices in another angular orientation.

[0062] FIGS. 14A-14C graphically illustrate a method of the invention incausing a wave of Rf energy density to propagate across and engagedtissue membrane to denature tissue constituents:

[0063]FIG. 14A being the engagement surface of FIG. 12 engaging tissuemembrane at the time that energy delivery is initiated causing localizedmicrocurrents and ohmic tissue heating;

[0064]FIG. 14B being the engagement surface of FIG. 12 after anarbitrary millisecond or microsecond time interval depicting thepropagation of a wavefronts of energy outward from the initial localizedmicrocurrents as the localized temperature and resistance of the matrixis increased; and

[0065]FIG. 14C being the engagement surface of FIG. 12 after anothervery brief interval depicting the propagation of the wavefronts ofenergy density outwardly in the tissue due to increase temperature andresistance of matrix portions.

[0066]FIG. 15 is an enlarged sectional view of the exemplary jawstructure of FIG. 13A with a plurality of opposing polarity conductorson either side of conductive-resistive matrix portions.

[0067]FIG. 16 is a sectional view of a jaw structure similar to that ofFIG. 15 with a plurality of opposing polarity conductors that floatwithin an elastomeric conductive-resistive matrix portions.

[0068]FIG. 17 is a sectional view of a jaw structure similar to that ofFIG. 16 with a single central conductor that floats on a convexelastomeric conductive-resistive matrix with opposing polarityconductors in outboard locations.

[0069] FIGS. 18A-18C provide simplified graphic views of the method ofcausing a wave of Rf energy density in the embodiment of FIG. 17,similar to the method shown in FIGS. 14A-14C:

[0070]FIG. 18A corresponding to the view of FIG. 14A showing initiationof energy delivery;

[0071]FIG. 18B corresponding to the view of FIG. 14B showing thepropagation of the wavefronts of energy density outwardly; and

[0072]FIG. 18C corresponding to the view of FIG. 14C showing the furtheroutward propagation of the wavefronts of energy density to thereby weldtissue.

[0073]FIG. 19 is a sectional view of another exemplary jaw structurethat carries two conductive-resistive matrix portions, each having adifferent durometer and a different temperature coefficient profile.

[0074]FIG. 20 is a sectional view of a jaw assembly having theengagement plane of FIG. 17 carried in a transecting-type jaws similarto that of FIGS. 3A-3B.

[0075]FIG. 21 is a sectional view of a portion of an exemplary Type “C”jaw structure with a conductive-resistive matrix system that containsvoids for controlling the overall thermal expansion envelope of thematrix.

[0076] FIGS. 22A-22B are enlarged sectional views of a portion of Type“C” jaw structure of FIG. 21 taken along line 22-22 of FIG. 21 showingthe method of operation of the conductive-resistive matrix system forcontrolling its overall thermal expansion;

[0077]FIG. 22A depicting the matrix at room temperature prior to use;and

[0078]FIG. 22B depicting the matrix at an elevated temperature duringuse showing the compression of the void spaces.

[0079]FIG. 23 is a sectional view of a portion of an alternative Type“C” jaw structure with a conductive-resistive matrix system togetherwith large scale open spaces for controlling the overall thermalexpansion of the matrix.

[0080]FIG. 24 is a sectional view of an alternative Type “C” jawstructure with a conductive-resistive matrix and a compressible materialor a negative coefficient of expansion material for controlling theoverall thermal expansion of the matrix.

[0081]FIG. 25 is a sectional view of an alternative Type “C” jaw withconductive-resistive matrices and expansion spaces as in FIG. 23together with means for supporting an island electrode.

DETAILED DESCRIPTION OF THE INVENTION

[0082] 1. Exemplary jaw structures for welding tissue. FIGS. 3A and 3Billustrate a working end of a surgical grasping instrument correspondingto the invention that is adapted for transecting captured tissue and forcontemporaneously welding the captured tissue margins with controlledapplication of Rf energy. The jaw assembly 100A is carried at the distalend 104 of an introducer sleeve member 106 that can have a diameterranging from about 2 mm. to 20 mm. for cooperating with cannulae inendoscopic surgeries or for use in open surgical procedures. Theintroducer portion 106 extends from a proximal handle (not shown). Thehandle can be any type of pistol-grip or other type of handle known inthe art that carries actuator levers, triggers or sliders for actuatingthe jaws and need not be described in further detail. The introducersleeve portion 106 has a bore 108 extending therethrough for carryingactuator mechanisms for actuating the jaws and for carrying electricalleads 109 a-109 b for delivery of electrical energy to electrosurgicalcomponents of the working end.

[0083] As can be seen in FIGS. 3A and 3B, the jaw assembly 100A hasfirst (lower) jaw element 112A and second (upper) jaw element 112B thatare adapted to close or approximate about axis 115. The jaw elements canboth be moveable or a single jaw can rotate to provide the jaw-open andjaw-closed positions. In the exemplary embodiment of FIGS. 3A and 3B,both jaws are moveable relative to the introducer portion 106.

[0084] Of particular interest, the opening-closing mechanism of the jawassembly 100A is capable of applying very high compressive forces ontissue on the basis of cam mechanisms with a reciprocating member 140.The engagement surfaces further provide a positive engagement of cammingsurfaces (i) for moving the jaw assembly to the (second) closed positionto apply very high compressive forces, and (ii) for moving the jawstoward the (first) open position to apply substantially high openingforces for “dissecting” tissue. This important feature allows thesurgeon to insert the tip of the closed jaws into a dissectable tissueplane-and thereafter open the jaws to apply such dissecting forcesagainst tissues. Prior art instruments are spring-loaded toward the openposition which is not useful for dissecting tissue.

[0085] In the embodiment of FIGS. 3A and 3B, a reciprocating member 140is actuatable from the handle of the instrument by any suitablemechanism, such as a lever arm, that is coupled to a proximal end 141 ofmember 140. The proximal end 141 and medial portion of member 140 aredimensioned to reciprocate within bore 108 of introducer sleeve 106. Thedistal portion 142 of reciprocating member 140 carries first (lower) andsecond (upper) laterally-extending flange elements 144A and 144B thatare coupled by an intermediate transverse element 145. The transverseelement further is adapted to transect tissue captured between the jawswith a leading edge 146 (FIG. 3A) that can be a blade or a cuttingelectrode. The transverse element 145 is adapted to slide within achannels 148 a and 148 b in the paired first and second jaws to therebyopen and close the jaws. The camming action of the reciprocating member140 and jaw surfaces is described in complete detail in co-pendingProvisional U.S. Patent Application Serial No. 60/347,382 filed Jan. 11,2002 (Docket No. SRX-013) titled Jaw Structure for ElectrosurgicalInstrument and Method of Use, which is incorporated herein by reference.

[0086] In FIGS. 3A and 3B, the first and second jaws 112A and 112B closeabout an engagement plane 150 and define tissue-engaging surface layers155A and 155B that contact and deliver energy to engaged tissues fromelectrical energy means as will be described below. The jaws can haveany suitable length with teeth or serrations 156 for gripping tissue.One preferred embodiment of FIGS. 3A and 3B provides such serrations 156at an inner portion of the jaws along channels 148 a and 148 b thusallowing for substantially smooth engagement surface layers 155A and155B laterally outward of the tissue-gripping elements. The axial lengthof jaws 112A and 112B indicated at L can be any suitable lengthdepending on the anatomic structure targeted for transection and sealingand typically will range from about 10 mm. to 50 mm. The jaw assemblycan apply very high compression over much longer lengths, for example upto about 200 mm., for resecting and sealing organs such as a lung orliver. The scope of the invention also covers jaw assemblies for aninstrument used in micro-surgeries wherein the jaw length can be about5.0 mm or less.

[0087] In the exemplary embodiment of FIGS. 3A and 3B, the engagementsurface 155A of the lower jaw 112A is adapted to deliver energy totissue, at least in part, through a conductive-resistive matrix CMcorresponding to the invention. The tissue-contacting surface 155B ofupper jaw 112B preferably carries a similar conductive-resistive matrix,or the surface can be a conductive electrode or and insulative layer aswill be described below. Alternatively, the engagement surfaces of thejaws can carry any of the energy delivery components disclosed inco-pending U.S. patent application Ser. No. 10/032,867 filed Oct. 22,2001 (Docket No. SRX-011) titled Electrosurgical Jaw Structure forControlled Energy Delivery and U.S. Prov. Patent Application Serial No.60/337,695 filed Dec. 3, 2001 (Docket No. SRX-012) titledElectrosurgical Jaw Structure for Controlled Energy Delivery, both ofwhich are incorporated herein by reference.

[0088] Referring now to FIG. 4, an alternative jaw structure 100B isshown with lower and upper jaws having similar reference numerals112A-112B. The simple scissor-action of the jaws in FIG. 4 has beenfound to be useful for welding tissues in procedures that do not requiretissue transection. The scissor-action of the jaws can apply highcompressive forces against tissue captured between the jaws to performthe method corresponding to the invention. As can be seen by comparingFIGS. 3B and 4, the jaws of either embodiment 100A or 100B can carry thesame energy delivery components, which is described next.

[0089] It has been found that very high compression of tissue combinedwith controlled Rf energy delivery is optimal for welding the engagedtissue volume contemporaneous with transection of the tissue.Preferably, the engagement gap g between the engagement planes rangesfrom about 0.0005″ to about 0.050″ for reduce the engaged tissue to thethickness of a membrane. More preferably, the gap g between theengagement planes ranges from about 0.001″ to about 0.005″.

[0090] 2. Type “A” conductive-resistive matrix system for controlledenergy delivery in tissue welding. FIG. 5 illustrates an enlargedschematic sectional view of a jaw structure that carries engagementsurface layers 155A and 155B in jaws 112A and 112B. It should beappreciated that the engagement surface layers 155A and 155B are shownin a scissors-type jaw (cf. FIG. 4) for convenience, and theconductive-resistive matrix system would be identical in each side of atransecting jaw structure as shown in FIGS. 3A-3B.

[0091] In FIG. 5, it can be seen that the lower jaw 112A carries acomponent described herein as a conductive-resistive matrix CM that isat least partly exposed to an engagement plane 150 that is defined asthe interface between tissue and a jaw engagement surface layer, 155A or155B. More in particular, the conductive-resistive matrix CM comprises afirst portion 160 a and a second portion 160 b. The first portion ispreferably an electrically nonconductive material that has a selectedcoefficient of expansion that is typically greater than the coefficientof expansion of the material of the second portion. In one preferredembodiment, the first portion 160 a of the matrix is an elastomer, forexample a medical grade silicone. The first portion 160 a of the matrixalso is preferably not a good thermal conductor. Other thermoplasticelastomers fall within the scope of the invention, as do ceramics havinga thermal coefficient of expansion with the parameters further describedbelow.

[0092] Referring to FIG. 5, the second portion 160 b of the matrix CM isa material that is electrically conductive and that is distributedwithin the first portion 160 a. In FIG. 5, the second portion 160 b isrepresented (not-to-scale) as spherical elements 162 that are intermixedwithin the elastomer first portion 160 a of matrix CM. The elements 162can have any regular or irregular shape, and also can be elongatedelements or can comprise conductive filaments. The dimensions ofelements 162 can range from nanoparticles having a scale of about 1 nm.to 2 nm. across a principal axis thereof to much larger cross-sectionsof about 100 microns in a typical jaw structure. In a very large jaw,the elements 162 in matrix CM can have a greater dimension that 100microns in a generally spherical form. Also, the matrix CM can carry asecond portion 160 b in the form of an intertwined filament (orfilaments) akin to the form of steel wool embedded within an elastomericfirst portion 160 a and fall within the scope the invention. Thus, thesecond portion 160 b can be of any form that distributes an electricallyconductive mass within the overall volume of the matrix CM.

[0093] In the lower jaw 112A of FIG. 5, the matrix CM is carried in asupport structure or body portion 158 that can be of any suitable metalor other material having sufficient strength to apply high compressiveforces to the engaged tissue. Typically, the support structure 158carries an insulative coating 159 to prevent electrical current flow totissues about the exterior of the jaw assembly and between supportstructure 158 and the matrix CM and a conductive element 165 therein.

[0094] Of particular interest, the combination of first and secondportions 160 a and 160 b provide a matrix CM that is variably resistive(in ohms-centimeters) in response to temperature changes therein. Thematrix composition with the temperature-dependent resistance isalternatively described herein as a temperature coefficient material. Inone embodiment, by selecting the volume proportion of first portion 160a of the non-conductive elastomer relative to the volume proportion ofsecond portion 160 b of the conductive nanoparticles or elements 162,the matrix CM can be engineered to exhibit very large changes inresistance with a small change in matrix temperature. In other words,the change of resistance with a change in temperature results in a“positive” temperature coefficient of resistance.

[0095] In a first preferred embodiment, the matrix CM is engineered toexhibit unique resistance vs. temperature characteristics that isrepresented by a positively sloped temperature-resistance curve (seeFIG. 6). More in particular, the first exemplary matrix CM indicated inFIG. 6 maintains a low base resistance over a selected base temperaturerange with a dramatically increasing resistance above a selected narrowtemperature range of the material (sometimes referred to herein as aswitching range, see FIG. 6). For example, the base resistance can below, or the electrical conductivity high, between about 37° C. and 65°C., with the resistance increasing greatly between about 65° C. and 75°C. to substantially limit conduction therethrough (at typically utilizedpower levels in electrosurgery). In a second exemplary matrix embodimentdescribed in FIG. 6, the matrix CM is characterized by a morecontinuously positively sloped temperature-resistance over the range of50° C. to about 80° C. Thus, the scope of the invention includes anyspecially engineered matrix CM with such a positive slope that issuitable for welding tissue as described below.

[0096] In one preferred embodiment, the matrix CM has a first portion160 a fabricated from a medical grade silicone that is doped with aselected volume of conductive particles, for example carbon particles insub-micron dimensions as described above. By weight, the ration ofsilicone-to-carbon can range from about 10/90 to about 70/30(silicone/carbon) to provide the selected range at which the inventivecomposition functions to substantially limit electrical conductancetherethrough. More preferably, the carbon percentage in the matrix CM isfrom about 40% to 80% with the balance being silicone. In fabricating amatrix CM in this manner, it is preferable to use a carbon type that hassingle molecular bonds. It is less preferable to use a carbon type withdouble bonds that has the potential of breaking down when used in asmall cross-section matrix, thus creating the potential of a permanentconductive path within deteriorated particles of the matrix CM that fusetogether. One preferred composition has been developed to provide athermal treatment range of about 75° C. to 80° C. with the matrix havingabout 50-60 percent carbon with the balance being silicone. The matrixCM corresponding to the invention thus becomes reversibly resistant toelectric current flow at the selected higher temperature range, andreturns to be substantially conductive within the base temperaturerange. In one preferred embodiment, the hardness of the silicone-basedmatrix CM is within the range of about Shore A range of less than about95. More preferably, an exemplary silicone-based matrix CM has Shore Arange of from about 20-80. The preferred hardness of the silicone-basedmatrix CM is about 150 or lower in the Shore D scale. As will bedescribed below, some embodiments have jaws that carry cooperatingmatrix portions having at least two different hardness ratings.

[0097] In another embodiment, the particles or elements 162 can be apolymer bead with a thin conductive coating. A metallic coating can bedeposited by electroless plating processes or other vapor depositionprocess known in the art, and the coating can comprise any suitablethin-film deposition, such as gold, platinum, silver, palladium, tin,titanium, tantalum, copper or combinations or alloys of such metals, orvaried layers of such materials. One preferred manner of depositing ametallic coating on such polymer elements comprises an electrolessplating process provided by Micro Plating, Inc., 8110 Hawthorne Dr.,Erie, Pa. 16509-4654. The thickness of the metallic coating can rangefrom about 0.00001″ to 0.005″. (A suitable conductive-resistive matrixCM can comprise a ceramic first portion 160 a in combination withcompressible-particle second portion 160 b of a such a metallizedpolymer bead to create the effects illustrated in FIGS. 8A-8B below).

[0098] One aspect of the invention relates to the use of a matrix CM asillustrated schematically in FIG. 5 in a jaw's engagement surface layer155A with a selected treatment range between a first temperature (TE₁)and a second temperature (TE₂) that approximates the targeted tissuetemperature for tissue welding (see FIG. 6). The selected switchingrange of the matrix as defined above, for example, can be anysubstantially narrow 1°-10° C. range that is about the maximum of thetreatment range that is optimal for tissue welding. For anotherthermotherpy, the switching range can fall within any larger tissuetreatment range of about 50°-200° C.

[0099] No matter the character of the slope of thetemperature-resistance curve of the matrix CM (see FIG. 6), a preferredembodiment has a matrix CM that is engineered to have a selectedresistance to current flow across its selected dimensions in the jawassembly, when at 37° C., that ranges from about 0.0001 ohms to 1000ohms. More preferably, the matrix CM has a designed resistance acrossits selected dimensions at 37° C. that ranges from about 1.0 ohm to 1000ohms. Still more preferably, the matrix CM has with a designedresistance across its selected dimensions at 37° C. that ranges fromabout 25 ohms to 150 ohms. In any event, the selected resistance acrossthe matrix CM in an exemplary jaw at 37° C. matches or slightly exceedsthe resistance of the tissue or body structure that is engaged. Thematrix CM further is engineered to have a selected conductance thatsubstantially limits current flow therethrough corresponding to aselected temperature that constitutes the high end (maximum) of thetargeted thermal treatment range. As generally described above, such amaximum temperature for tissue welding can be a selected temperaturebetween about 50° C. and 90° C. More preferably, the selectedtemperature at which the matrix's selected conductance substantiallylimits current flow occurs at between about 60° C. and 80° C.

[0100] In the exemplary jaw 112A of FIG. 5, the entire surface area ofengagement surface layer 155A comprises the conductive-resistive matrixCM, wherein the engagement surface is defined as the tissue-contactingportion that can apply electrical potential to tissue. Preferably, anyinstrument's engagement surface has a matrix CM that comprises at least5% of its surface area. More preferably, the matrix CM comprises atleast 10% of the surface area of engagement surface. Still morepreferably, the matrix CM comprises at least 20% of the surface area ofthe jaw's engagement surface. The matrix CM can have any suitablecross-sectional dimensions, indicated generally at md₁ and md₂ in FIG.5, and preferably such a cross-section comprises a significantfractional volume of the jaw relative to support structure 158. As willbe described below, in some embodiments, it is desirable to provide athermal mass for optimizing passive conduction of heat to engagedtissue.

[0101] As can be seen in FIG. 5, the interior of jaw 112A carries aconductive element (or electrode) indicated at 165 that interfaces withan interior surface 166 of the matrix CM. The conductive element 165 iscoupled by an electrical lead 109 a to a voltage (Rf) source 180 andoptional controller 182 (FIG. 4). Thus, the Rf source 180 can applyelectrical potential (of a first polarity) to the matrix CM throughconductor 165—and thereafter to the engagement plane 150 through matrixCM. The opposing second jaw 112B in FIG. 5 has a conductive material(electrode) indicated at 185 coupled to source 180 by lead 109 b that isexposed within the upper engagement surface 155B.

[0102] In a first mode of operation, referring to FIG. 5, electricalpotential of a first polarity applied to conductor 165 will result incurrent flow through the matrix CM and the engaged tissue et to theopposing polarity conductor 185. As described previously, the resistanceof the matrix CM at 37° C. is engineered to approximate, or slightlyexceed, that of the engaged tissue et. It can now be described how theengagement surface 155A can modulate the delivery of energy to tissue etsimilar to the hypothetical engagement surface of FIG. 2. Consider thatthe small sections of engagement surfaces represent the micron-sizedsurface areas (or pixels) of the illustration of FIG. 2 (note that thejaws are not in a fully closed position in FIG. 5). The preferredmembrane-thick engagement gap g is graphically represented in FIG. 5.

[0103]FIGS. 7A and 8A illustrate enlarged schematic sectional views ofjaws 112A and 112B and the matrix CM. It can be understood that theelectrical potential at conductor 165 will cause current flow within andabout the elements 162 of second portion 160 b along any conductive pathtoward the opposing polarity conductor 185. FIG. 8A more particularlyshows a graphic representation of paths of microcurrents mc_(m) withinthe matrix wherein the conductive elements 162 are in substantialcontact. FIG. 7A also graphically illustrates paths of microcurrentsmc_(t) in the engaged tissue across gap g. The current paths in thetissue (across conductive sodium, potassium, chlorine ions etc.) thusresults in ohmic heating of the tissue engaged between jaws 112A and112B. In fact, the flux of microcurrents mc_(m) within the matrix andthe microcurrents met within the engaged tissue will seek the mostconductive paths—which will be assisted by the positioning of elements162 in the surface of the engagement layer 155A, which can act likesurface asperities or sharp edges to induce current flow therefrom.

[0104] Consider that ohmic heating (or active heating) of the shadedportion 188 of engaged tissue et in FIGS. 7B and 8B elevates itstemperature to a selected temperature at the maximum of the targetedrange. Heat will be conducted back to the matrix portion CM proximate tothe heated tissue. At the selected temperature, the matrix CM willsubstantially reduce current flow therethrough and thus will contributeless and less to ohmic tissue heating, which is represented in FIGS. 7Band 8B. In FIGS. 7B and 8B, the thermal coefficient of expansion of theelastomer of first matrix portion 160 a will cause slight redistributionof the second conductive portion 160 b within the matrix—naturallyresulting in lessened contacts between the conductive elements 162. Itcan be understood by arrows A in FIG. 8B that the elastomer will expandin directions of least resistance which is between the elements 162since the elements are selected to be substantially resistant tocompression.

[0105] Of particular interest, the small surface portion of matrix CMindicated at 190 in FIG. 8A will function, in effect, independently tomodulate power delivery to the surface of the tissue T engaged thereby.This effect will occur across the entire engagement surface layer 155A,to provide practically infinite “spatially localized” modulation ofactive energy density in the engaged tissue. In effect, the engagementsurface can be defined as having “pixels” about its surface that areindependently controlled with respect to energy application to localizedtissue in contact with each pixel. Due to the high mechanicalcompression applied by the jaws, the engaged membrane all can beelevated to the selected temperature contemporaneously as each pixelheats adjacent tissue to the top of treatment range. As also depicted inFIG. 8B, the thermal expansion of the elastomeric matrix surface alsowill push into the membrane, further insuring tissue contact along theengagement plane 150 to eliminate any possibility of an energy arcacross a gap.

[0106] Of particular interest, as any portion of theconductive-resistive matrix CM falls below the upper end of targetedtreatment range, that matrix portion will increase its conductance andadd ohmic heating to the proximate tissue via current paths through thematrix from conductor 165. By this means of energy delivery, the mass ofmatrix and the jaw body will be modulated in temperature, similar to theengaged tissue, at or about the targeted treatment range.

[0107]FIG. 9 shows another embodiment of a conductive-resistive matrixCM that is further doped with elements 192 of a material that is highlythermally conductive with a selected mass that is adapted to providesubstantial heat capacity. By utilizing such elements 192 that may notbe electrically conductive, the matrix can provide greater thermal massand thereby increase passive conductive or convective heating of tissuewhen the matrix CM substantially reduces current flow to the engagedtissue. In another embodiment (not shown) the material of elements 162can be both substantially electrically conductive and highly thermallyconductive with a high heat capacity.

[0108] The manner of utilizing the system of FIGS. 7A-7B to perform themethod of the invention can be understood as mechanically compressingthe engaged tissue et to membrane thickness between the first and secondengagement surfaces 155A and 155B of opposing jaws and thereafterapplying electrical potential of a frequency and power level known inelectrosurgery to conductor 165, which potential is conducted throughmatrix CM to maintain a selected temperature across engaged tissue etfor a selected time interval. At normal tissue temperature, the low baseresistance of the matrix CM allows unimpeded Rf current flow fromvoltage source 180 thereby making 100 percent of the engagement surfacean active conductor of electrical energy. It can be understood that theengaged tissue initially will have a substantially uniform impedance toelectrical current flow, which will increase substantially as theengaged tissue loses moisture due to ohmic heating. Following anarbitrary time interval (in the microsecond to ms range), the impedanceof the engaged tissue—reduced to membrane thickness—will be elevated intemperature and conduct heat to the matrix CM. In turn, the matrix CMwill constantly adjust microcurrent flow therethrough—with each squaremicron of surface area effectively delivering its own selected level ofpower depending on the spatially-local temperature. This automaticreduction of localized microcurrents in tissue thus prevents anydehydration of the engaged tissue. By maintaining the desired level ofmoisture in tissue proximate to the engagement plane(s), the jawassembly can insure the effective denaturation of tissue constituents tothereafter create a strong weld.

[0109] By the above-described mechanisms of causing the matrix CM to bemaintained in a selected treatment range, the actual Rf energy appliedto the engaged tissue et can be precisely modulated, practicallypixel-by-pixel, in the terminology used above to describe FIG. 2.Further, the elements 192 in the matrix CM can comprise a substantialvolume of the jaws' bodies and the thermal mass of the jaws, so thatwhen elevated in temperature, the jaws can deliver energy to the engagedtissue by means of passive conductive heating—at the same time Rf energydelivery in modulated as described above. This balance of active Rfheating and passive conductive heating (or radiative, convectiveheating) can maintain the targeted temperature for any selected timeinterval.

[0110] Of particular interest, the above-described method of theinvention that allows for immediate modulation of ohmic heating acrossthe entirety of the engaged membrane is to be contrasted with prior artinstruments that rely on power modulation based on feedback from atemperature sensor. In systems that rely on sensors or thermocouples,power is modulated only to an electrode in its totality. Further, theprior art temperature measurements obtained with sensors is typicallymade at only at a single location in a jaw structure, which cannot beoptimal for each micron of the engagement surface over the length of thejaws. Such temperature sensors also suffer from a time lag. Stillfurther, such prior art temperature sensors provide only an indirectreading of actual tissue temperature—since a typical sensor can onlymeasure the temperature of the electrode.

[0111] Other alternative modes of operating the conductive-resistivematrix system are possible. In one other mode of operation, the systemcontroller 182 coupled to voltage source 180 can acquire data fromcurrent flow circuitry that is coupled to the first and second polarityconductors in the jaws (in any locations described previously) tomeasure the blended impedance of current flow between the first andsecond polarity conductors through the combination of (i) the engagedtissue and (ii) the matrix CM. This method of the invention can providealgorithms within the system controller 182 to modulate, or terminate,power delivery to the working end based on the level of the blendedimpedance as defined above. The method can further include controllingenergy delivery by means of power-on and power-off intervals, with eachsuch interval having a selected duration ranging from about 1microsecond to one second. The working end and system controller 182 canfurther be provided with circuitry and working end components of thetype disclosed in Provisional U.S. Patent Application Serial No.60/339,501 filed Nov. 9, 2001 (Docket No. S-BA-001) titledElectrosurgical Instrument, which is incorporated herein by reference.

[0112] In another mode of operation, the system controller 182 can beprovided with algorithms to derive the temperature of the matrix CM frommeasured impedance levels—which is possible since the matrix isengineered to have a selected unique resistance at each selectedtemperature over a temperature-resistance curve (see FIG. 6). Suchtemperature measurements can be utilized by the system controller 182 tomodulate, or terminate, power delivery to engagement surfaces based onthe temperature of the matrix CM. This method also can control energydelivery by means of the power-on and power-off intervals as describedabove.

[0113] FIGS. 10-11 illustrate a sectional views of an alternative jawstructure 100C-in which both the lower and upper engagement surfaces155A and 155B carry a similar conductive-resistive matrices indicated atCMA and CMB. It can be easily understood that both opposing engagementsurfaces can function as described in FIGS. 7A-7B and 8A-8B to applyenergy to engaged tissue. The jaw structure of FIGS. 10-1 I illustratethat the tissue is engaged on opposing sides by a conductive-resistivematrix, with each matrix CM_(A) and CM_(B) in contact with an opposingpolarity electrode indicated at 165 and 185, respectively. It has beenfound that providing cooperating first and second conductive-resistivematrices in opposing first and second engagement surfaces can enhanceand control both active ohmic heating and the passive conduction ofthermal effects to the engaged tissue.

[0114] 3. Type “B” conductive-resistive matrix system for tissuewelding. FIGS. 12 and 14A-14C illustrate an exemplary jaw assembly 200that carries a Type “B” conductive-resistive matrix system for (i)controlling Rf energy density and microcurrent paths in engaged tissue,and (ii) for contemporaneously controlling passive conductive heating ofthe engaged tissue. The system again utilizes an elastomericconductive-resistive matrix CM although substantially rigidconductive-resistive matrices of a ceramic positive-temperaturecoefficient material are also described and fall within the scope of theinvention. The jaw assembly 200 is carried at the distal end of anintroducer member, and can be a scissor-type structure (cf. FIG. 4) or atransecting-type jaw structure (cf. FIGS. 3A-3B). For convenience, thejaw assembly 200 is shown as a scissor-type instrument that allows forclarity of explanation.

[0115] The Type “A” system and method as described above in FIGS. 5 and7A-7B allowed for effective pixel-by-pixel power modulation—whereinmicroscale spatial locations can be considered to apply an independentpower level at a localized tissue contact. The Type “B”conductive-resistive matrix system described next not only allows forspatially localized power modulation, it additionally provides for thetiming and dynamic localization of Rf energy density in engagedtissues—which can thus create a “wave” or “wash” of a controlled Rfenergy density across the engaged tissue reduced to membrane thickness.

[0116] Of particular interest, referring to FIG. 12, the Type “B” systemaccording to the invention provides an engagement surface layer of atleast one jaw 212A and 212B with a conductive-resistive matrix CMintermediate a first polarity electrode 220 having exposed surfaceportion 222 and second polarity electrode 225 having exposed surfaceportion 226. Thus, the microcurrents within tissue during a briefinterval of active heating can flow to and from said exposed surfaceportions 222 and 226 within the same engagement surface 255A. Byproviding opposing polarity electrodes 220 and 225 in an engagementsurface with an intermediate conductive-resistive matrix CM, it has beenfound that the dynamic “wave” of energy density (ohmic heating) can becreated that proves to be a very effective means for creating a uniformtemperature in a selected cross-section of tissue to thus provide veryuniform protein denaturation and uniform cross-linking on thermalrelaxation to create a strong weld. While the opposing polarityelectrodes 220 and 225 and matrix CM can be carried in both engagementsurfaces 255A and 255B, the method of the invention can be more clearlydescribed using the exemplary jaws of FIG. 11 wherein the upper jaw'sengagement surface 250B is an insulator indicated at 252.

[0117] More in particular, referring to FIG. 12, the first (lower) jaw212A is shown in sectional view with a conductive-resistive matrix CMexposed in a central portion of engagement surface 255A. A firstpolarity electrode 220 is located at one side of matrix CM with thesecond polarity electrode 225 exposed at the opposite side of the matrixCM. In the embodiment of FIG. 12, the body or support structure 258 ofthe jaw comprises the electrodes 220 and 225 with the electrodesseparated by insulated body portion 262. Further, the exterior of thejaw body is covered by an insulator layer 261. The matrix CM isotherwise in contact with the interior portions 262 and 264 ofelectrodes 220 and 225, respectively.

[0118] The jaw assembly also can carry a plurality of alternatingopposing polarity electrode portions 220 and 225 with intermediateconductive-resistive matrix portions CM in any longitudinal, diagonal ortransverse arrangements as shown in FIGS. 13A-13C. Any of thesearrangements of electrodes and intermediate conductive-resistive matrixwill function as described below at a reduced scale—with respect to anypaired electrodes and intermediate matrix CM.

[0119] FIGS. 14A-14C illustrate sequential views of the method of usingof the engagement surface layer of FIG. 11 to practice the method of theinvention as relating to the controlled application of energy to tissue.For clarity of explanation, FIGS. 14A-14C depict exposed electrodesurface portions 220 and 225 at laterally spaced apart locations with anintermediate resistive matrix CM that can create a “wave” or “front” ofohmic heating to sweep across the engaged tissue et. In FIG. 14A, theupper jaw 212B and engagement surface 250B is shown in phantom view, andcomprises an insulator 252. The gap dimension g is not to scale, asdescribed previously, and is shown with the engaged tissue having asubstantial thickness for purposes of explanation.

[0120]FIG. 14A provides a graphic illustration of the matrix CM withinengagement surface layer 250A at time T₁—the time at which electricalpotential of a first polarity (indicated at +) is applied to electrode220 via an electrical lead from voltage source 180 and controller 182.In FIGS. 14A-14C, the spherical graphical elements 162 of the matrix arenot-to-scale and are intended to represent a “region” of conductiveparticles within the non-conductive elastomer 164. The graphicalelements 162 thus define a polarity at particular microsecond in timejust after the initiation of power application. In FIG. 14A, the bodyportion carrying electrode 225 defines a second electrical potential (−)and is coupled to voltage source 180 by an electrical lead. As can beseen in FIG. 14A, the graphical elements 162 are indicated as having atransient positive (+) or negative (−) polarity in proximity to theelectrical potential at the electrodes. When the graphical elements 162have no indicated polarity (see FIGS. 14B & 14C), it means that thematrix region has been elevated to a temperature at the matrix switchingrange wherein electrical conductance is limited, as illustrated in thatpositively sloped temperature-resistance curve of FIG. 6 and thegraphical representation of FIG. 8B.

[0121] As can be seen in FIG. 14A, the initiation of energy applicationat time T₁ causes microcurrents mc within the central portion of theconductive matrix CM as current attempts to flow between the opposingpolarity electrodes 220 and 225. The current flow within the matrix CMin turn localizes corresponding microcurrents mc′ in the adjacentengaged tissue et. Since the matrix CM is engineered to conductelectrical energy thereacross between opposing polarities at about thesame rate as tissue, when both the matrix and tissue are at about 37°C., the matrix and tissue initially resemble each other, in anelectrical sense. At the initiation of energy application at time T₁,the highest Rf energy density can be defined as an “interface” indicatedgraphically at plane P in FIG. 14A, which results in highly localizedohmic heating and denaturation effects along that interface whichextends from the matrix CM into the engaged tissue. Thus, FIG. 14Aprovides a simplified graphical depiction of the interface or plane Pthat defines the “non-random” localization of ohmic heating anddenaturation effects—which contrasts with all prior art methods thatcause entirely random microcurrents in engaged tissue. In other words,the interface between the opposing polarities wherein active Rf heatingis precisely localized can be controlled and localized by the use of thematrix CM to create initial heating at that central tissue location.

[0122] Still referring to FIG. 14A, as the tissue is elevated intemperature in this region, the conductive-resistive matrix CM in thatregion is elevated in temperature to its switching range to becomesubstantially non-conductive (see FIG. 6) in that central region.

[0123]FIG. 14B graphically illustrates the interface or plane P at timeT₂—an arbitrary microsecond or millisecond time interval later than timeT₁. The dynamic interface between the opposing polarities wherein Rfenergy density is highest can best be described as planes P and P′propagating across the conductive-resistive matrix CM and tissue thatare defined by “interfaces” between substantially conductive andnon-conductive portions of the matrix—which again is determined by thelocalized temperature of the matrix. Thus, the microcurrent mc′ in thetissue is indicated as extending through the tissue membrane with thehighest Rf density at the locations of planes P and P′. Stated anotherway, the system creates a front or wave of Rf energy density thatpropagates across the tissue. At the same time that Rf density (ohmicheating) in the localized tissue is reduced by the adjacent matrix CMbecoming nonconductive, the matrix CM will begin to apply substantialthermal effects to the tissue by means of passive conductive heating asdescribed above.

[0124]FIG. 14C illustrates the propagation of planes P and P′ at timeT₃—an additional arbitrary time interval later than T₂. Theconductive-resistive matrix CM is further elevated in temperature behindthe interfaces P and P′ which again causes interior matrix portions tobe substantially less conductive. The Rf energy densities thus propagatefurther outward in the tissue relative to the engagement surface 255A asportions of the matrix change in temperature. Again, the highest Rfenergy density will occur at generally at the locations of the dynamicplanes P and P′. At the same time, the lack of Rf current flow in themore central portion of matrix CM can cause its temperature to relax tothus again make that central portion electrically conductive. Theincreased conductivity of the central matrix portion again is indicatedby (+) and (−) symbols in FIG. 14C. Thus, the propagation of waves of Rfenergy density will repeat itself as depicted in FIGS. 14A-14C which caneffectively weld tissue.

[0125] Using the methods described above for controlled Rf energyapplication with paired electrodes and a conductive-resistive matrix CM,it has been found that time intervals ranging between about 500 ms and4000 ms can be sufficient to uniformly denature tissue constituentsre-crosslink to from very strong welds in most tissues subjected to highcompression. Other alternative embodiments are possible that multiplythe number of cooperating opposing polarity electrodes 220 and 225 andintermediate or surrounding matrix portions CM.

[0126]FIG. 15 depicts an enlarged view of the alternative Type “B” jaw212A of FIG. 13A wherein the engagement surface 250A carries a pluralityof exposed conductive matrix portions CM that are intermediate aplurality of opposing polarity electrode portions 220 and 225. Thislower jaw 212A has a structural body that comprises the electrodes 220and 225 and an insulator member 266 that provide the strength requiredby the jaw. An insulator layer 261 again is provided on outer surfacesof the jaw excepting the engagement surface 255A. The upper jaw (notshown) of the jaw assembly can comprise an insulator, aconductive-resistive matrix, an active electrode portion or acombination thereof. In operation, it can be easily understood that eachregion of engaged tissue between each exposed electrode portion 222 and226 will function as described in FIGS. 14A-14C.

[0127] The type of engagement surface 250A shown in FIG. 15 can haveelectrode portions that define an interior exposed electrode width ewranging between about 0.005″ and 0.20″ with the exposed outboardelectrode surface 222 and 226 having any suitable dimension. Similarly,the engagement surface 250A has resistive matrix portions that portionsthat define an exposed matrix width mw ranging between about 0.005″ and0.20″.

[0128] In the embodiment of FIG. 15, the electrode portions 220 and 225are substantially rigid and extend into contact with the insulatormember 266 of the jaw body thus substantially preventing flexing of theengagement surface even though the matrix CM may be a flexible siliconeelastomer. FIG. 16 shows an alternative embodiment wherein the electrodeportions 220 and 225 are floating within, or on, the surface layers ofthe matrix 250A.

[0129]FIG. 17 illustrates an alternative Type “B” embodiment that isadapted for further increasing passive heating of engaged tissue whenportions of the matrix CM are elevated above its selected switchingrange. The jaws 212A and 212B and engagement surface layers 255A and255B both expose a substantial portion of matrix to the engaged tissue.The elastomeric character of the matrix can range between about 20 and95 in the Shore A scale or above about 40 in the Shore D scale.Preferably, one or both engagement surface layers 255A and 255B can be“crowned” or convex to insure that the elastomeric matrices CM tend tocompress the engaged tissue. The embodiment of FIG. 17 illustrates thata first polarity electrode 220 is a thin layer of metallic material thatfloats on the matrix CM and is bonded thereto by adhesives or any othersuitable means. The thickness of floating electrode 220 can range fromabout 1 micron to 200 microns. The second polarity electrode 225 hasexposed portions 272 a and 272 b at outboard portions of the engagementplanes 255A and 255B. In operation, the jaw structure of FIG. 17 createscontrolled thermal effects in engaged tissue by several different means.First, as indicated in FIGS. 18A-18C, the dynamic waves of Rf energydensity are created between the opposing polarity electrode portions 220and 225 and across the intermediate matrix CM exactly as describedpreviously. Second, the electrically active components of the upperjaw's engagement surface layer 255B cause microcurrents between theengagement surface layers 255A and 255B, as well as to the outboardexposed electrode surfaces exposed portions 272 a and 272 b, between anyportions of the matrices that are below the selected switching range.Third, the substantial volume of matrix CM is each jaw providessubstantial heat capacity to very rapidly cause passive heating oftissue after active tissue heating is reduced by increasing impedance inthe engaged tissue et.

[0130]FIG. 19 illustrates another Type “B” embodiment of jaws structurethat again is adapted for enhanced passive heating of engaged tissuewhen portions of the matrix CM are elevated above its selected switchingrange. The jaws 212A and 212B and engagement surface layers 255A and255B again expose matrix portions to engaged tissue. The upper jaw'sengagement surface layer 255B is convex and has an elastomeric hardnessranging between about 20 and 80 in the Shore A scale and is fabricatedas described previously.

[0131] Of particular interest, the embodiment of FIG. 19 depicts a firstpolarity electrode 220 that is carried in a central portion ofengagement plane 255A but the electrode does not float as in theembodiment of FIG. 17. The electrode 220 is carried in a first matrixportion CM₁ that is a substantially rigid silicone or can be a ceramicpositive temperature coefficient material. Further, the first matrixportion CM₁ preferably has a differently sloped temperature-resistanceprofile (cf. FIG. 6) that the second matrix portion CM₂ that is locatedcentrally in the jaw 212A. The first matrix portion CM₁, whethersilicone or ceramic, has a hardness above about 90 in the Shore A scale,whereas the second matrix portion CM₂ is typically of a silicone asdescribed previously with a hardness between about 20 and 80 in theShore A scale. Further, the first matrix portion CM₁ has a higherswitching range than the second matrix portion CM₂. In operation, thewave of Rf density across the engaged tissue from electrode 220 tooutboard exposed electrode portions 272 a and 272 b will be induced bymatrix CM₁ having a first higher temperature switching range, forexample between about 70° C. to 80° C., as depicted in FIGS. 18A-18C.The rigidity of the first matrix CM₁ prevents flexing of the engagementplane 255A. During use, passive heating will be conducted in an enhancedmanner to tissue from electrode 220 and the underlying second matrix CM₂which has a second selected lower temperature switching range, forexample between about 60° C. to 70° C. This Type “B” system has beenfound to be very effective for rapidly welding tissue-in part because ofthe increased surface area of the electrode 220 when used in smallcross-section jaw assemblies (e.g., 5 mm. working ends).

[0132]FIG. 20 shows the engagement plane 255A of FIG. 17 carried in atransecting-type jaws assembly 200D that is similar to that of FIGS.3A-3B. As described previously, the Type “B” conductive-resistive matrixassemblies of FIGS. 12-19 are shown in a simplified form. Any of theelectrode-matrix arrangements of FIGS. 12-19 can be used in thecooperating sides of a jaw with a transecting blade member-similar tothe embodiment shown in FIG. 20.

[0133] 3. Type “C” system. FIGS. 21 and 22A-22B illustrate an exemplaryType “C” jaw assembly 500A that is similar to that of FIGS. 17, 19 and20. In co-pending U.S. patent application Ser. No. 10/032,867 filed Oct.22, 2001 (Docket No. SRX-011) titled Electrosurgical Jaw Structure forControlled Energy Delivery, a conductive matrix CM that exhibitsvariable resistance based on its temperature is disclosed wherein thematrix is an open-cell or closed-cell foam type material. The embodimentof FIGS. 21 and 22A-22B illustrates an embodiment of such aconductive-resistive matrix CM that carries voids or encapsulated gasvolumes and thereby can be designed to provide a selected degree ofthermal expansion of the overall matrix envelope due to thecompressibility of the voids within the matrix. These types ofconductive-resistive matrices CM that contain compressible gas volumesor bubbles are sometimes described herein as aeratedconductive-resistive matrices CM.

[0134] In one preferred embodiment, the first portion 160 a of matrix CMthat is substantially non-conductive can be a silicone as describedpreviously. The second portion 160 b that is conductive again can becarbon particles or any suitable metallic particles. In anotherembodiment, the second conductive portion 160 b can be filaments on anysuitable dimension that are of a shape memory material such as an alloyof nickel and titanium as is known in the art. Upon heating to aselected temperature range, the material can undergo a crystallinetransformation from its martensitic phase to its austhenitic or memoryphase. The memory shape of such a shape memory material can be designedto assist in enhancing or diminishing conductivity in a matrix as thematrix volume is elevated in temperature.

[0135] The substantially non-conductive first portion 160 a can comprisematerials other than silicone, for example a thermosetting polymer suchas a polyester, phenolic or epoxy or a thermoplastic polymer such aspolyethelene or polypropylene. More specifically, suitable materials forfirst portion 160 a of a matrix CM include, besides silicone, apolytetrafluoroethylene (PTFE) or a polyperfluoroalkoethylene such as aDuPont Kalrez® Compound, an Ausimont Hyflon® Fluoropolymer, or a DupontTeflon® material. The suitable materials for first component 160 a of amatrix CM have a coefficient of thermal expansion that differssubstantially from the coefficient of thermal expansion of the secondconductive component 160 b of the matrix. More in particular, a suitablefirst component 160 a of a matrix CM has a coefficient of thermalexpansion that ranges between about 10⁻³ mm./° C. to about 10⁻⁶ mm./° C.

[0136] The Type “C” system of FIG. 21 depicts a portion of jaws 512A and512B similar to that disclosed in FIG. 17. The lower jaw 512A carries afirst polarity (+) floating electrode 520 as in FIG. 17 with an aeratedconductive-resistive matrix CM at an interior of the jaw body withportions of the matrix exposed in the engagement surface 555A. The upperjaw 512B and engagement surface 555B can of any type described above inFIGS. 17 and 19, or can comprise an insulated surface as described inFIGS. 14A-14C. Preferably, the upper engagement surface layer 555B isslightly convex and of an elastomeric matrix as seen in FIG. 17. Again,both jaws have structural body portions 558 a and 558 b of a conductorwith exterior surfaces coated with a thin insulator layer 561. Thesebody portions 558 a and 558 b are coupled to electrical source 180 todefine a second polarity (−) therein with exposed surface portions 572 aand 572 b in the jaw's engagement planes serving as electrode portionsthat contact lateral portions of the engaged tissue.

[0137] The schematic view of the jaws in FIG. 21 depicts aconductive-resistive matrix CM that is similar to that describedpreviously (see FIGS. 7A-8B) and comprises a first non-conductivecomposition 160 a and a second conductive composition 160 b distributedtherein. In addition, the conductive-resistive matrix CM carries a thirdportion indicated at 566 that comprises a selected proportion of voidsor encapsulated gas volumes to provide an aerated conductive-resistivematrix. The voids or aerated portions 566 of the matrix CM thus play therole of an expansion chamber to accommodate the expansion of the firstnon-conductive composition 160 a of the matrix. It has been found thatit is useful to precisely control the overall thermal expansion envelopeof a conductive-resistive matrix CM, particularly in small diameterinstruments. This is particularly important where the matrix CM iscarried in a channel within a jaw body. In many embodiments, a slightexpansion of the matrix CM typically is desirable to assist in applyingcompressive forces to the engaged tissue. Preferably, the design of thejaws structure is adapted to precisely control all functionalparameters, including the matrix's overall thermal expansion envelope.The thermal expansion envelope of the matrix will vary substantiallydepending upon the material chosen for the first nonconductive portion160 a of the matrix. Thus, the selection of a particular proportion ofthe matrix volume to be voids can provide means for controlling theoverall expansion envelope of the matrix. In one embodiment, the aeratedportion of the matrix ranges from zero to about fifty percent of theoverall matrix volume (or envelope) at room temperature. Morepreferably, the aerated or open portion of the matrix ranges from two totwenty-five percent of the overall matrix volume at room temperature.Still more preferably, the open portion of the matrix CM ranges fromfive to fifteen percent of the overall matrix volume at roomtemperature. These preferred ranges have been investigated in thefabrication of conductive-resistive matrices of silicone as describedpreviously. These gas volumes can be introduced into a liquid siliconematerial by mechanical stirring before “setting” the final shape of thematerial. The gas bubbles can range in size from sub-micron scalebubbles to voids about 1 mm. in diameter. The bubble also could beproduced by chemical reactants or solvent evaporation.

[0138] FIGS. 22A-22B provide schematic illustrations of the manner inwhich the aerated matrix CM of the invention functions in operation. Forexample, FIG. 22A schematically shows the third portion of the matrix oraerated portion 566 as a selected proportion of voids or bubbles ofparticular dimensions at room temperature before delivering energy tothe engaged tissue indicated at t (phantom view). Next, FIG. 22B depictsthe matrix CM with the first portion 160 a expanding at an increasedtemperature thereof which in turn tends to collapse the voids (seearrows) at the same time that the matrix increases its resistance whichcontrols Rf energy density and current paths in the engaged tissue, andcontemporaneously controls passive conductive heating of the engagedtissue t.

[0139]FIG. 23 illustrates an alternative embodiment of jaw assembly 500Bthat is similar to FIG. 19 that again provides means for accommodatingthe expansion of a conductive-resistive matrix CM within a jaw body. Inthis embodiment, at least one relatively large open space 576 isprovided at an interior of the jaw to allow for expansion of the matrixupon heating. Such open spaces can have any suitable dimension andconfiguration to control the overall exterior dimensional envelope ofthe matrix CM and floating electrode 520.

[0140] In yet another embodiment 500C shown in FIG. 24, the means forcontrolling the thermal expansion envelope of the matrix CM need not beactual open spaces as depicted in FIG. 23, but the matrix CM can beadjacent to one or more portions 568 of a solid but resilientcompressible material that cooperates with the matrix to controllablycompress upon thermal expansion of the matrix to thereby control theexterior dimensional envelope of the matrix and floating electrode 520.In another embodiment that is similar to FIG. 24 (not shown), the matrixCM can cooperate with another material that has a negative thermalcoefficient of expansion as is known in the art. In this variation, suchmaterial will shrink in volume as it is elevated in temperature toaccommodate any thermal expansion of the conductive-resistive matrix CM.

[0141] In another embodiment 500D depicted in FIG. 25, an interior ofthe jaw can be configured with blocks 582 of non-matrix material, forexample a substantially rigid insulative material, for supporting thefloating type electrode indicated at 520. It cases wherein the matrix CMis of a compressible material or open cell material, it has been founduseful to support a central conductor 520 on a rigid pedestal form thatotherwise did not interfere with the functioning of the matrix CM. FIG.25 again shows voids or open spaces 576 that allow for expansion of thematrix portions CM. In a jaw structure with voids 576, such as theembodiments of FIG. 25 or FIG. 23, it has been found useful to provideat least one vent indicated at 586(FIG. 25) in the jaw body thatcommunicates with void 576. Such a vent 586 allows for expansion of thematrix CM without compressing the gas trapped in the void. The use of avent 586 also can be useful in an aerated open-cell matrix CM similar tothe embodiment of FIGS. 21 and 22A-22B.

[0142] Although particular embodiments of the present invention havebeen described above in detail, it will be understood that thisdescription is merely for purposes of illustration. Specific features ofthe invention are shown in some drawings and not in others, and this isfor convenience only and any feature may be combined with another inaccordance with the invention. Further variations will be apparent toone skilled in the art in light of this disclosure and are intended tofall within the scope of the appended claims.

What is claimed is:
 1. An electrosurgical jaw structure for controlledapplication of energy to tissue, comprising: first and second jawsmovable between opened and closed positions, each jaw defining anengagement surface layer for contacting tissue; at least one engagementsurface layer carrying first and second conductors operatively coupledto an electrical source to define opposing polarities therein; said atleast one engagement surface layer carrying a matrix materialintermediate the first and second conductors, the matrix materialcomprising first and second compositions each in a selected proportionof the matrix volume, the first composition being substantiallynon-conductive electrically and the second composition beingelectrically conductive and dispersed within first composition, andwherein the first and second compositions define different selectedcoefficients of thermal expansion to thereby provide the matrix with aresistance that varies with temperature.
 2. The jaw structure of claim 1wherein said first composition is an elastomer.
 3. The jaw structure ofclaim 1 wherein said first composition is a silicone.
 4. The jawstructure of claim 1 wherein said first composition is a thermoplasticpolymer.
 5. The jaw structure of claim 1 wherein said first compositionis a ceramic.
 6. The jaw structure of claim 1 further comprising aplurality of voids in an interior of the matrix material for controllingthe thermal expansion envelope of the matrix material.
 7. The jawstructure of claim 1 further comprising at least one void in an interiorof the jaw structure proximate to the matrix material for controllingthe thermal expansion envelope of the matrix material.
 8. The jawstructure of claim 7 further comprising at least one vent in the jawstructure communicating with said at least one void.
 9. The jawstructure of claim 1 further comprising at least one portion ofcompressible material within the jaw and within the matrix material forcontrolling the thermal expansion envelope of the matrix material. 10.The jaw structure of claim 1 further comprising at least one portion ofa material defining a negative thermal coefficient of expansionproximate to or within the matrix material for controlling the thermalexpansion envelope of the matrix material.
 11. The jaw structure ofclaim 1 wherein the second composition is a conductive particle having adimension across a principal axis ranging between about 1 nanometer and1000 microns.
 12. The jaw structure of claim 1 wherein the secondcomposition is a conductive particle having a dimension across aprincipal axis ranging between about 1 nanometer and 100 microns. 13.The jaw structure of claim 1 wherein the second composition is aconductive particle having a dimension across a principal axis rangingbetween about 1 nanometer and 10 microns.
 14. The jaw structure of claim1 wherein the second composition is a conductive filament.
 15. The jawstructure of claim 14 wherein the conductive filament is of a shapememory material.
 16. An electrosurgical jaw structure for controlledapplication of energy to tissue, comprising: first and second jawsmovable between opened and closed positions, the jaws defining first andsecond engagement surface layers respectively for contacting tissue; thefirst engagement surface layer carrying a matrix material that defines apositively sloped temperature coefficient of resistance; a firstconductor in contact with the matrix material, said first conductorcoupled to an electrical energy source to define a first polaritytherein during operation; and a second conductor exposed in the secondengagement surface layer, said second conductor coupled to saidelectrical energy source to define a second polarity therein duringoperation.
 17. The electrosurgical jaw structure of claim 16 furthercomprising: a third conductor exposed the first engagement surface layerspaced apart from the first conductor, said third conductor coupled tosaid electrical energy source to define said second polarity therein;wherein the matrix material is intermediate the first conductor andthird conductor in the first engagement surface layer.
 18. Theelectrosurgical jaw structure of claim 16 wherein the first conductor issurrounded on at least two sides in the first engagement surface by thematrix material.
 19. The electrosurgical jaw structure of claim 16wherein the first conductor comprises an island on a layer of the matrixmaterial.
 20. The electrosurgical jaw structure of claim 16 furthercomprising matrix thermal expansion control means within the interior ofthe jaw for controlling the dimensional envelope of the matrix materialupon its elevation in temperature.
 21. The electrosurgical jaw structureof claim 20 wherein said matrix thermal expansion control meanscomprises a volume of voids dispersed with the matrix material.
 22. Theelectrosurgical jaw structure of claim 20 wherein said matrix thermalexpansion control means comprises at least one air gap within aninterior of the jaw proximate to said matrix material.
 23. Theelectrosurgical jaw structure of claim 20 wherein said matrix thermalexpansion control means comprises at least one material within orproximate to the matrix that is compressible in response to thermalexpansion of the matrix material.
 24. The electrosurgical jaw structureof claim 20 wherein said matrix thermal expansion control meanscomprises at least one material with a negative temperature coefficientof expansion within or proximate to the matrix.
 25. An electrosurgicalinstrument for controllably causing ohmic heating of tissue, comprising:an instrument having a body that defines an engagement surface forengaging tissue; the engagement surface carrying an electricalconductor; and an interior portion of the body comprising a matrix incontact with said electrical conductor, the matrix coupled to anelectrical source wherein the matrix defines a positive temperaturecoefficient of resistance for controlling current flow therethrough, andwherein the matrix or body defines voids therein for controlling theoverall dimensional expansion of the matrix in the body of theinstrument.
 26. The electrosurgical instrument of claim 25 wherein thebody carries at least one vent that communicates with said voids. 27.The electrosurgical instrument of claim 25 wherein the voids comprisegas bubbles ranging in size from a sub-micron diameter to about 1 mm. indiameter.
 28. The electrosurgical instrument of claim 25 wherein theengagement surface is carried in at least one of a pair of jaw membersthat are moveable between open and closed positions.
 29. Theelectrosurgical instrument of claim 25 wherein the matrix is at leastpartly an elastomeric composition.
 30. The electrosurgical instrument ofclaim 25 wherein the matrix is at least partly a ceramic composition.31. The electrosurgical instrument of claim 25 wherein the matrix is atleast partly a thermoset material.
 32. The electrosurgical instrument ofclaim 25 wherein the matrix is an open cell composition.
 33. Theelectrosurgical instrument of claim 25 wherein the matrix is a closedcell composition.
 34. An electrosurgical method for controllingapplication of energy to a tissue site, comprising the steps of: (a)providing a working end that defines an engagement surface forcontacting tissue, said engagement surface comprising in part atemperature coefficient matrix material that defines a positively-slopedtemperature-resistance curve over a selected temperature range, theworking end carrying first and second spaced apart conductorsoperatively connected to an electrical source that defines first andsecond polarities in said conductors, said matrix material positionedintermediate said first and second conductors; (b) positioning theengagement surface in contact with tissue; and (c) causing Rf currentflow from the first polarity conductor to the second polarity conductorthrough the engaged tissue and said matrix material thereby causingohmic heating in the engaged tissue; (d) wherein said ohmic heating inthe engaged tissue is modulated as the temperature of said matrixmaterial changes and alters the resistance thereof to thereby modulateand redirect current paths in said matrix material and said engagedtissue.
 35. The method of claim 34 wherein said matrix material definesa temperature-resistance curve that continuously increases over aselected temperature range of about 37° C. to 100° C. and wherein step(d) continuously modulates energy application when the temperature ofthe said matrix material and the engaged tissue is within said selectedtemperature range.
 36. An electrosurgical instrument comprising: anintroducer member extending along a longitudinal axis; first and secondjaws carried at a distal end of said introducer, said jaws definingfirst and second engagement surfaces respectively for contacting tissue,said engagement surfaces moveable relative to each other from an openposition to a closed position for engaging tissue, a portion of thefirst engagement surface comprising a conductor that defines a firstpolarity therein; a portion of the second engagement surface comprisinga conductor that defines a second polarity therein; an interior of atleast one jaw carrying a matrix material in contact with the conductor,the matrix material having a resistance to electrical current flow thatincreases with the temperature thereof.
 37. The electrosurgicalinstrument of claim 36 wherein said matrix material has a resistance tocurrent flow when at 37° C. ranging from about 0.0001 ohms to 1000 ohms.38. The electrosurgical instrument of claim 36 wherein said matrixmaterial has a resistance to current flow when at 37° C. ranging fromabout 1.0 ohm to 500 ohms.
 39. The electrosurgical instrument of claim36 wherein said matrix material has a resistance to current flow when at37° C. ranging from about 25 ohms to 150 ohms.